The present invention is based on Japanese Patent Applications No. 2000-198501, each content of which being incorporated by reference.
1. Field of the Invention
The present invention relates to a so-called tandem-type color image forming apparatus.
2. Description of the Related Art
A so-called tandem-type color image forming apparatus is conventionally known in which a plurality of image forming units storing toners of different colors are arranged along an intermediate transfer belt, as disclosed in Japanese laid-open Patent Application No. HEI 7-28294.
With such an image forming apparatus, images of respective colors are formed, one upon another, on the intermediate transfer belt in respective image forming units, and the resulting composite color image is transferred from the transfer belt onto a sheet due to a voltage applied to a transfer roller.
However, when the transfer roller is eccentric relative to its rotation shaft, it causes fluctuation in a rotation speed of the intermediate transfer belt. As a result, color deviation may occur when the image forming units superimpose images of respective colors one upon another on the intermediate transfer belt.
It is, therefore, an object of the present invention to provide an image forming apparatus which is capable of preventing color deviation of an image even when a transfer roller is eccentric.
A color image forming apparatus in accordance with the present invention comprises: an intermediate transfer member having a movable surface; a plural image forming units for forming toner images on the intermediate transfer member at each of image-forming positions; and a transfer roller for transferring the toner images formed on the intermediate transfer member onto a sheet, the transfer roller having a circumferential length equal to the distance between adjacent image forming positions.
In the image forming apparatus according to the present invention, the circumferential length of the transfer roller is made equal to the distance between adjacent image forming positions. Therefore, even when the transfer roller is eccentric and hence the rotation speed of the intermediate transfer member fluctuates, the rotation speed of the intermediate transfer member is the same at the times when respective image forming means form respective color images at a point of the intermediate transfer member. As a result, it is possible to form an image on the intermediate transfer member without causing color deviation.